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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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188                                 ALASKAN GLACIER STUDIES
needed to wait only a short time to witness large ice falls from the glacier front; but in our visit of 1909 we rarely saw or heard such ice falls, and the fiord in front of the glacier was far freer from floating ice than in former years.
Viewed from OUT photographic sites on the north side of Nunatak Fiord, the Nunatak Glacier presented even more notable changes. In 1909 the width of the glacier at the terminus was only f of a mile and the marginal projections noted in 1905 were entirely gone (PI. LXVIt, B). The middle projection was also destroyed and the glacier front extended in an almost straight line from the north side to a point two-thirds of the way across the fiord where there was a very slight projection, beyond which the ice front receded. There was also a striking difference in position of the three medial moraines.
In 1905 (PI. LXVH, A) these moraines entered the sea near the middle of the glacier. In 1909 they were all over in the southern half of the glacier. The black medial moraine caused by the union of the two arms of the Nunatak Glacier entered the sea in the southern quarter of the glacier front. The reason for this change in position of the medial moraines is explained by the appearance of a bulging of the ice surface across the southern arm where the nunatak hill extends beneath the glacier. It was evident that the southern tributary had been so diminished in activity that its surface had been lowered by ablation until t.Tiia subglacial rock barrier became effective enough to cut off a considerable part of the supply that the southern arm formerly contributed to the tidal end of Nunatak Glacier. With t.hia diminution in supply from the southern tributary, the still vigorous northern arm was able to thrust the medial moraines farther and farther toward the south.
Another noteworthy evidence of recession was clearly brought out from the photographic sites which were established on the alluvial fans on the north side of the fiord a short distance from sea level. From one viewpoint (Sta. F, Map 4) the front of the ice cliff was so near in 1905 that it hid the glacier so that we could not see much of its surface. Possibly also the ice cliff was higher than now. In 1909, on the other hand, from these same positions we were able to look up on the ice surface for a considerable distance. From this point of view it was seen in 1909 that back of its ice cliff the glacier rose in a series of steps; and the rise was so rapid in the lower mile that it seemed certain that not much more recession would be needed to transform this tidal glacier to one resting on the land. At the rate of recession going on in 1909 it would have been surprising if the Nunatak Glacier had been still tidal at the end of another ten years or even less.
The rapid recession of Nunatak Glacier between 1891 and 1909 seems to be part of a recession of much greater extent, perhaps continuous, perhaps interrupted by halts and readvances, but certainly never interrupted by any long period of halting. The evidence of the former extension of Nunatak Glacier until it coalesced with Hidden Glacier, and reached far up Russell Fiord, has been stated in the reports on our 1905 and 1906 expeditions, and will not be repeated here. That the complete recession from this former extension of the glacier has occurred in a brief time, is proved by the condition of vegetation which is now advancing to reoccupy the area from which the glacier has so recently receded. Positive and definite evidence of the amount of recession for a portion of the distance has just been stated in comparison of the photographic records of 1895, 1899, 1905, 1906, 1909 and 1910. The 1899 photographs by Gilbert show clearly the position of the ice edge in that year, and in 1905, 1909 and 1910 some of the ice still remained in a stagnant, debris-covered mass, detached from the main glacier and lying in about the position occupied in 1899 by the outermost moraine-covered northern edge of